MFRC522 Pin Confusion

Other Hardware Sensors
1

I am working on a system involving an EBay version of the MFRC522 RFID card scanner. The card claims to have several communication interfaces, and the Miguel Balboa library for the scanner implements the SPI interface, including a MOSI, MISO, SCK, and SS pin. The version of this scanner that I bought does not have a pin labeled SS (slave select), but has an SDA pin, probably for the I2C interface. If SS is not present, does that imply the chip considers itself selected all the time, or does the SDA pin represent SS in this case?

Thanks in advance for any help.

2

SDA is the data line for I2C. There should be an SCL for a clock line.
I2C slaves listen for their address to be broadcast and then reply with acknowledge bit, There is not a discrete chip select like SPI uses.

3

I will assume, for this scanner, that it internally has slave selected all the time, but I won't know for sure until I receive the scanner. At any rate, the Balboa library requires that an SS pin be designated for the initialization. As usual, the devil is in the details.